Generally, when a substrate made of such a brittle material as glass is scribed and broken, it is widely used to form a scribing line on the surface of a substrate by rolling a cutter wheel in close contact with the substrate surface, and to break the substrate by generating a crack in the direction of thickness of the substrate along the scribe line. The scribing and breaking for a brittle material is hereinafter referred to as “cutting” for short.
The cutter wheel for scribing a substrate is made of a cemented carbide and sintered diamond, especially a cutter wheel made of sintered diamond is widely used in view of life of a cutter. Such a cutter wheel (hereinafter referred to as “wheel” in this invention) has a peripheral ridge extending equiangularly, i.e. cutting edges, and has a penetrating axis hole by which the wheel is supported rataionally on a substrate. Further, outer diameter is sometimes set to be 2 to 3 mm in order to increase load per unit area at the contact point of cutter of the surface of a substrate.
On the other hand, the present applicant has filed a patent application for a wheel which has contiguous protrusions and grooves with a predetermined space therebetween in the circumferential direction on the cutter (cf. Patent Reference 1).
According to this patent, when a scribe line is formed on the surface of a substrate by protrusions of a cutter, a deep vertical crack can be formed in the direction of thickness of the substrate and at the same time slip at the moment of rolling the wheel can be effectively prevented. The above-mentioned protrusions and grooves are machined with a diamond wheel. The “diamond wheel” is a grindstone specified in JIS-B4131 in the broad sense of the term. In order to avoid confusion with the term “wheel” (a cutter wheel) in this invention, it is hereinafter referred to as “grindstone”.
[Patent Reference 1]
Japanese Patent No. 3074143